The W3C I18N WG/IG, together with the W3C XML Core WG,
are aware of the situation and are working on the relevant
errata for this. Our current plans are to make some fixes
(to make clear that XML parsers should not enforce Production 35,
in order to be forward-compatible) as soon as time permits, and
the rest (updating from RFC 1766 to its successor) as soon as
that is out.